The present invention relates to a bicycle front fork, and relates more particularly to a shock absorbing mechanism for the front fork of a bicycle.
The fork blades of the front fork of a bicycle are commonly and respectively made in two parts, namely, the upper cylindrical casing and the lower cylindrical casing. The upper cylindrical casing has a top end fastened to the blade holder of the front fork and a bottom end fastened with an upper spring holder made to slide in the lower cylindrical casing. The lower cylindrical casing is supported on either end of the front wheel axle of the bicycle, having a lower spring holder fastened on the inside. A compression spring is received inside the lower cylindrical casing and retained between the upper spring holder and the lower spring holder. Because only the compression spring is provided to absorb shocks and the compression spring is made uniform in diameter, the shock absorbing ability is not sufficient. Further, if the compression spring is made of metal, it will rub against the inside wall of the lower cylindrical casing producing noises when the bicycle suddenly runs over an uneven road surface. If the compression spring is made of plastics (for example: polyurethane), it can not effectively absorb shocks as the bicycle moves over a continuously rugged road surface. As the upper cylindrical casing is made to slide in the lower cylindrical casing, the outside surface of the upper cylindrical casing frequently rubs against the inside surface of the lower cylindrical casing, causing the upper and lower cylindrical casings to wear out quickly. Because the upper cylindrical casing and the lower cylindrical casing are linked together simply by the compression springs, the upper cylindrical casing may jump out of the lower cylindrical casing, causing an accident to happen. Therefore, this structure of bicycle front fork is not safe in use. Still another drawback of this structure of bicycle front fork is that the spring force of the compression spring in either fork blade of the front fork can not be regulated. If spring force of the compression springs in the two fork blades of the front fork are not in balance due to different elastic fatique after long uses, the compression springs must be replaced. Still another drawback of this structure of bicycle front fork is that the lower cylindrical casing is complicated to manufacture. As the lower cylindrical casing is made of an aluminum alloy through a forging process, it must be made having a tapered inside wall so that it can be conveniently removed from the forging die. After the process of forging, the tapered inside wall of the lower cylindrical casing must be processed again so that the upper cylindrical casing can slide within the inside wall of the lower cylindrical casing. This complicated processing process greatly increases the manufacturing cost and time of the bicycle front fork. A yet further drawback of this structure of bicycle front fork is that there is not any guide means to guide the compression spring as the compression spring is compressed, therefore the compression spring will rub against the inside wall of the lower cylindrical casing causing noises to happen. As the compression spring is frequently forced to rub against the inside wall of the lower cylindrical casing, it may be damaged easily.
The present invention has been accomplished to provide a bicycle front fork shock absorbing mechanism which eliminates the aforesaid problems. According to the preferred embodiment of the present invention, the bicycle front fork shock absorbing mechanism comprises a lower cylindrical casing having a lower rubber ring above an inside screw hole thereof and a friction lining around the inside wall thereof, an upper cylindrical casing inserted into the lower cylindrical casing to hold a stack of upper rubber rings by a locating block, a friction ring mounted around the lower cylindrical casing in contact with the friction lining through a slide contact, a shock absorbing conical spring retained between the upper rubber rings and the lower rubber ring, and a screw rod having a head stopped above the locating block. The screw rod is inserted in proper order through a hole on the locating block, the upper rubber rings, the shock absorbing conical spring, and the lower rubber ring and then threaded into the screw hole on the lower cylindrical casing. The arrangement of the friction lining inside the lower cylindrical casing eliminates the processing process to grind the inside wall of the lower cylindrical casing. The arrangement of the upper and lower rubber rings and the shock absorbing conical spring effectively absorb shocks of different frequencies in different directions. The slide contact between the friction lining on the lower cylindrical casing and the friction ring on the upper cylindrical casing eliminates noises during the relative movement between the upper and lower cylindrical casings. Further, the arrangement of the headed adjusting screw rod permits the spring force of the shock absorbing conical spring to be adjustable, and simultaneously guide the shock absorbing conical spring in course as the shock absorbing conical spring is alternatively compressed and released.